X and Y-axis of the ultimaker

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Here is an explanation I found trying to explain the X and Y-axis movement in an Ultimaker.

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X-axis and Y-axis

These printers have a hotend that is moved on both the X and Y-axis at the same time or independently. Both of the X and Y-axis have a linear rail that they move along. The X and Y-axis are affixed to the printer and do not move up or down. Imagine looking down at one axis. It would look like an H. The center part of the H is what moves up and down and the other axis would be the exact same, except sideways. The hotend is connected to both of the center rails at a fixed point. If you move both axis at the same time from one end to the other, the hotend will move in a diagonal motion. Otherwise, each axis will move the hotend along it’s path if it’s the only one being moved.

There are 2 belts each for both the X and Y-axis. They are connected together via a moving rod that spins along with that axis of movement. At both ends of the rod, a GT2 Gear is connected. On the opposite side of the belts, there are bearings that allow free movement of the belts. The belts are connected at the point where the bearing of the axis moves along the linear rail. This way, the rod or rail is moved at both ends at the same time, resulting in a consistent movement. Any flex is eliminated that may occur from only one end of the rail moving. That flex would end up with horribly misshapen prints.

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I understand the Ultimaker has a complicated x and y-axis movement. I wanted a mechanical/electrical explanation of how this process works. In the quote I posted; the article tried to explain it but it still isn't clear. I don't own any Ultimaker to make this observation myself. I hope this is clear.

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Our print head can only move through x and y (so left-right and back-forth). Our build plate moves in z (so up-down).

Our build plate is connected to a threaded axis, which pushes it up and down, this is pretty straightforward.

The print head has 2 rods crossing through it. Each of these rods is connected to another axle which runs parallel to the frame. The fixture that holds these rods, is also connected to a belt. That belt is responsible for transferring movement it receives from a motor located somewhere else, and the axle that goes parallel to the frame functions only as a guide for direction.

This video has some good shots of how it works. Feel free to browse around on our youtube channel for more video's and references.

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Correction to Sander's above post - the origin is always at the front left corner although some of the UM printers do their homing at the rear left corner but that corner is considered Y value around e.g. 225mm.

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I think for mechanical you need a picture so I'd look at that video posted above.

For the electrical - a simplistic explanation. There are two coils in the stepper. Each coil has 2 wires going to it. Call the coils A and B. A is on the outside and B is on the inside part that rotates. We put sine waves of voltage and current through these coils. Not sure the frequency typically. If you shift the phase of the two sine waves of electricity it starts rotating the stepper. Once you move completely back into phase again that is one "step". UM steppers are I believe 200 steps per full rotation. Because of the gearing they are 5 steps/mm. There is something called "microstepping" or substepping. The stepper driver chip takes care of setting the frequency and the phase between the A and B signals. If you have 16 steps microstepping (as UM printers use for X and Y - I think Z is usually 8 microsteps) then that's 80 steps/mm. The driver shifts the phase by 16 steps. Since there are 360 degrees of possible phase shift put out between the A and B signals, 360/16 is 22.5 degrees so each time you do a microstep, the stepper chip increments by 22.5 degrees the phase between A and B.

The arduino only sends 2 digital signals to the stepper driver: direction, step. If direction is high it moves the servo one way, if direction is low it moves the servo the other way. Each pulse on the step pin moves one microstep. So 80 pulses would be 1mm.

This is very simplified explanation. I'll leave it to you to summarize even more simply.

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